The present invention relates to fuel injectors and, in particular, to a method and apparatus for controlling an injector needle stroke to minimize opening and closing impact forces.
An electromagnetic fuel injector utilizes a solenoid assembly to supply an actuating force to a fuel metering valve. Typically, a plunger style armature supporting a fuel injector needle reciprocates between a closed position, where the needle is closed to prevent fuel from escaping through the discharge orifice, and a fully open position, where fuel is discharged through the discharge orifice.
When the solenoid is energized, the solenoid armature, and thus the injector needle, is magnetically drawn from the closed position toward the fully open position by a solenoid generated magnetic flux. Typically, the solenoid is energized until the armature reaches its fully opened position and a period of time thereafter to discharge a desired amount of fuel. As the armature reaches the top of its stroke, it impacts an armature stop generating impact noise and resulting in the armature bouncing against the armature stop. This bouncing has detrimental effects on flow characteristics of the fuel.
When an appropriate amount of fuel has been discharged from the injector, the solenoid is de-energized, and the armature and injector needle are urged toward the closed position by the force of a spring. Similar to the top of the armature stroke, when the armature reaches the bottom of its stroke and the injector needle is seated to close the discharge orifice, the velocity of the injector needle generates impact noise against the seat and is subject to significant bouncing. The occurrence of such bouncing will typically result in an extra amount of unscheduled fuel being injected from the fuel injector into the engine, and this extra fuel can have an adverse effect on fuel economy and engine exhaust constituents.
Various means for eliminating such bouncing have been proposed, including those found in commonly assigned U.S. Pat. Nos. 4,878,650, 5,033,716 and 5,139,224.